Method for positioning, a positioning system, and an electronic device

ABSTRACT

A method for positioning a wireless communication device includes storing position data relating to one or a plurality of reference areas to at least one data base. It is examined which of said reference areas is located in the vicinity of the wireless communication device, and at least position data about the reference area located in the vicinity of the wireless communication device is retrieved for the wireless communication device. In order to perform the positioning, the method further includes selecting the reference area located in the vicinity of the wireless communication device as the default position of the wireless communication device.

This is a Continuation In Part application of U.S. patent applicationSer. No. 10/081,294, filed on Feb. 21, 2002, which claims priority fromFinnish patent application 20010365 filed on Feb. 23, 2001.

FIELD OF THE INVENTION

The present invention relates to a method for positioning of a wirelesscommunication device. The invention further relates to a positioningsystem to be used in the positioning of a wireless communication device.The invention relates also to an electronic device to be used in apositioning system, which electronic device comprises at leastpositioning means and mobile communication means. The invention alsorelates to a wireless communication device, and a method for deliveringassistance data for positioning of a wireless communication device.

BACKGROUND OF THE INVENTION

In positioning systems based on satellite positioning, a positioningreceiver attempts to receive signals of at least four satellites inorder to detect the position of the positioning receiver and the timedata. An example of such a satellite positioning system is the GPSsystem (Global Positioning System) comprising a plurality of satellitesorbiting the globe according to predefined orbits. These satellitestransmit positioning data, on based of which the position of a satellitecan be defined at each moment of time, in case the exact time data usedin the satellite positioning system is known in the positioningreceiver. In the GPS system, the satellites transmit a spread spectrumsignal which is modulated with a code that is individual for eachsatellite. Thus, the positioning receiver can distinguish signalstransmitted by different satellites from each other by using a referencecode corresponding to the satellite code generated locally in thepositioning receiver.

A drawback with such positioning systems based on satellite positioningis often the fact that a signal transmitted by a satellite is stronglyattenuated when arriving to the positioning receiver, wherein it is verydifficult to distinguish the signal from the background noise. Thesignal can be attenuated inter alia due to climatic conditions andobstacles, such as buildings and surrounding grounds in the routing ofthe signal. Also, the signal can wander to the positioning receiverthrough a plurality of different routes which causes so-called multipathpropagation and aggravates the synchronizing of the positioning receiverto a wished signal because the transmitted signal arrives to thereceiver through different routings, for example straight from thesatellite (line-of-sight) and, in addition to this; reflected. Due tothis multipath propagation the same signal is received as a plurality ofsignals with different phases. It is particularly difficult to performpositioning inside a building, because a building itself stronglyattenuates the signal transmitted by satellites and, on the other hand,multipath propagation can be even stronger since possibly reflectedsignals coming for example through a window are not necessarily asattenuated as signals coming straight through the roof. In this case,the receiver can make erroneous interpretations about the time of flightand the positioning of the satellite during the moment of transmission,inter alia due to said increase in the signal time-of-flight caused bymultipath propagation

Each operating satellite of the GPS system transmits a so-called L1signal in the carrier frequency of 1575.42 MHz. This frequency is alsoindicated with 154 f₀, where f₀=10.23 MHz. Furthermore, the satellitestransmit another ranging signal at a carrier frequency of 1227.6 MHzcalled L2,i.e. 120 f₀. In the satellite, these signals are modulatedwith at least one pseudo random sequence. This pseudo random sequence isdifferent for each satellite. As a result of the modulation, acode-modulated wideband signal is produced. The modulation techniqueused makes it possible to distinguish in the receiver the signalstransmitted by different satellites, even though the carrier frequenciesused in the transmission are substantially the same. This modulationtechnique is called code division multiple access (CDMA). In eachsatellite, for modulating the L1 signal, the pseudo sequence used ise.g. a so-called C/A code (Coarse/Acquisition code), which is a codefrom the family of the Gold codes. Each GPS satellite transmits a signalby using an individual C/A code. The codes are formed as a modulo-2 sumof two 1023-bit binary sequences. The first binary sequence G1 is formedwith a polynome X¹⁰+X³+1, and the second binary sequence G2 is formed bydelaying the polynome X¹⁰+X⁹+X⁸+X⁶+X³+X²+1 in such a way that the delayis different for each satellite. This arrangement makes it possible toproduce different C/A codes by an identical code generator. The C/Acodes are thus binary codes of which, chipping rate in the GPS system is1.023 MHz. The C/A code comprises 1023 chips, wherein the iteration time(epoch) of the code is 1 ms. The carrier wave of the L1 signal isfurther modulated by navigation information at a bit rate of 50 bit/s.The navigation information comprises information about the “health”,orbit, time data of the satellite, etc.

During their operation, the satellites monitor the condition of theirequipment. The satellites may use for example so-called watchdogoperations to detect and report possible faults in the equipment. Theerrors and malfunctions can be instantaneous or longer lasting. On thebasis of the health data, some of the faults can possibly be compensatedfor, or the information transmitted by a malfunctioning satellite can betotally disregarded. Furthermore, in a situation in which the signal ofmore than four satellites can be received, the information received fromdifferent satellites can be weighted differently on the basis of thehealth data. Thus, it is possible to minimize the effect of errors onmeasurements, possibly caused by satellites which seem unreliable.

To detect the signals of the satellites and to identify the satellites,the receiver must perform acquisition, whereby the receiver searches forthe signal of each satellite at the time and attempts to be synchronizedand locked to this signal so that the data transmitted with the signalcan be received and demodulated.

The positioning receiver must perform the acquisition e.g. when thereceiver is turned on and also in a situation in which the receiver hasnot been capable of receiving the signal of any satellite for a longtime.

Such a situation can easily occur e.g. in portable devices, because thedevice is moving and the antenna of the device is not always in anoptimal position in relation to the satellites, which impairs thestrength of the signal coming in the receiver.

The positioning arrangement has two primary functions:

-   -   1. to calculate the pseudorange between the receiver and the,        different GPS satellites, and    -   2. to determine the position of the receiver by utilizing the        calculated pseudoranges and the position data of the satellites.        The current position data of the satellites can be calculated on        the basis of the Ephemeris and time correction data received        from the satellites.

Distances to the satellites are called pseudoranges, because the time isnot accurately known in the receiver. Thus, the determinations ofposition and time are repeated until a sufficient accuracy is achievedwith respect to time and position. Because the time is not known withabsolute precision, the position and the time must be determined e.g. bylinearizing a set of equations for each new iteration.

A pseudorange can be calculated by measuring the pseudo transmissiontime delays between signals of different satellites.

Almost all known GPS receivers utilize correlation methods foracquisition to the code as well as for tracking. In a positioningreceiver, reference codes ref(k), i.e. the pseudo random sequences fordifferent satellites are stored or generated locally. A received signalis subjected to conversion to an intermediate frequency (downconversion), whereafter the receiver multiplies the received signal withthe stored pseudo random sequence. The signal obtained as a result ofthe multiplication is integrated or low-pass filtered, wherein theresult obtained is data about whether the received signal contained asignal transmitted by a satellite. The multiplication is iterated in thereceiver so that the phase of the pseudo random sequence stored in thereceiver is shifted each time. The correct phase is inferred from thecorrelation result for example so that when the correlation result is atits peak, the correct phase has been detected. Thus, the receiver iscorrectly synchronized with the received signal. After the codeacquisition has been completed, the next steps are frequency tuning andphase locking.

The above-mentioned acquisition and frequency control process must beperformed for each signal of a satellite received in the receiver. Somereceivers may include several receiving channels, wherein an attempt ismade on each receiving channel to be synchronized with the signal of onesatellite at a time and to detect the information transmitted by thissatellite.

The positioning receiver receives information transmitted by satellitesand performs positioning on the basis of the received information. Forthe positioning, the receiver must receive a signal transmitted by atleast four different satellites to find out the x, y, z coordinates andthe time data. The received navigation information is stored in amemory, wherein this stored information can be used to find out e.g. thepositioning data of satellites.

FIG. 1 shows, in a principle chart, positioning, by means of a signaltransmitted from four satellites SV1, SV2, SV3, SV4 in a wirelesscommunication device MS comprising a positioning receiver. In the GPSsystem, the satellites transmit positioning data as well as time data,on the basis of which the positioning receiver can perform calculationsto determine the current position of the satellite. These positioningdata and time data are transmitted in frames which are further dividedinto subframes. In the GPS system, each frame comprises 1500-bits, whichare divided into five subframes of 300 bits each. Since the transmissionof one bit takes 20 ms, the transmission of each subframe thus takes 6s, and the whole frame is transmitted in 30 seconds. The subframes arenumbered from 1 to 5. In each sub-frame 1, e.g. time data istransmitted, indicating the moment of transmission of the subframe aswell as information about the deviation of the satellite clock withrespect to the time in the GPS system. The subframes 2 and 3 are usedfor the transmission of positioning data. The subframe 4 contains othersystem information, such as universal time, coordinated (UTC). Thesubframe 5 is intended for the. transmission of almanac data of all thesatellites. The entity of these subframes and frames is called a GPSnavigation message which comprises 25 frames, i.e. 125 subframes. Thelength of the navigation message is thus 12 min 30 s.

In the GPS system, time is measured in seconds from the beginning of aweek. In the GPS system, the starting time of a week is the midnightbetween a Saturday and a Sunday. Each subframe to be transmittedcontains information on the moment of the GPS week when the subframe inquestion was transmitted. Thus, the time data indicates the time oftransmission of a certain bit, i.e. in the GPS system, the time oftransmission of the last bit-in the subframe in question. In thesatellites, time is measured with high-precision atomic chronometers. Inspite of this, the operation of each satellite is controlled in acontrol centre for the GPS system (not shown), and e.g. a timecomparison is performed to detect chronometric errors in the satellitesand to transmit this information to the satellite.

In the precision of positioning it is of great importance how preciselythe actual GPS time is known by the receiver. In practice, the preciseGPS time can be determined after positioning calculation, in which thechronometric error of the receiver is determined relative to the GPStime. However, in the very first positioning calculation an estimationof the GPS time can be used, because the actual GPS time, is notnecessarily known in the receiver. The estimated GPS time at a moment oftime k can be derived on the basis of measurement of three time elementsaccording to the following formula:T _(GPS) ^(j)(k)=T _(TOW)(k)+T _(ms) ^(j)(k)+T _(chip) ^(j)(k)+0.078  (1)in which

-   -   T_(TOW) ^(j)=the time data (time of week) in seconds contained        in the last received subframe,    -   T_(ms) ^(j)(k)=the time in seconds corresponding to the number        of C/A epochs received after the beginning of the last received        subframe,    -   T_(chip) ^(j)(k)=the time in seconds corresponding to the number        (from 0 to 1022) and code phase of whole chips received after        the change of the last epoch, and    -   j=the receiving channel index.

In Formula 1, the average time of flight (ToF) of the signal from thesatellite to the receiver is 78 ms. As a reference it is possible to useany such receiving channel in which the signal-to-noise ratio (SNR) issufficient.

The time data (ToW) is transmitted in the navigation message atintervals of six seconds and it indicates the time passed from the lastchange of the GPS week. Thus, the value range of the time data is theremainder of one week. In a corresponding manner T_(ms) ^(j)(k) equalsthe remainder of six seconds and T_(chip) ^(j)(k) equals the remainderof 1 ms.

The first three terms of the Formula (1) can also be used in themeasurement of the time of arrival (ToA) of the signal.

In poor receiving conditions in which the navigation data cannot beindicated inter alia due to a high bit error rate (BER), it is notpossible, due to the missing time data ToW, to determine the GPS timedirectly by means of the Formula 1. However, the code phase can normallystill be measured.

The first three terms in the Formula 1 determine the time oftransmission {circumflex over (T)}_(ToT) ^(k) of the received signal.

SUMMARY OF THE INVENTION

The present invention provides a positioning method and a positioningreceiver in which the location of a known reference point is used as thedefault location of the positioning receiver. The location of the knownreference point can be detected in a data base, or the like. The database can be arranged in a data network, such as the Internet networkand/or a mobile communication network. Moreover, the positioning data ofone or a plurality of reference points can be stored into an electronicdevice comprising a positioning receiver. The invention is based on theidea that the position of a such reference point of which position isknown is used as the default position of the electronic device, and theposition of the reference point is stored in the data base, wherein thispositioning data is retrieved from the data base to the electronicdevice. In case the positioning data are not stored in the electronicdevice, they are retrieved at the time when the positioning is wished tobe performed.

According to a first aspect of the present invention there is provided amethod for positioning of a wireless communication device, the methodcomprising:

-   -   storing position data relating to one or a plurality of        reference areas to at least one data base,    -   examining which of said reference areas is located in the        vicinity of the wireless communication device, and    -   retrieving at least position data about said reference area        located in the vicinity of the wireless communication device,    -   wherein in order to perform the positioning, the method further        comprises selecting said reference area located in the vicinity        of the wireless communication device as the default position of        the wireless communication device.

According to a second aspect of the present invention there is provideda positioning system to be used in the positioning of a wirelesscommunication device, the positioning system comprising:

-   -   at least one data base for storing one or a plurality of        reference areas, means for detecting which of said reference        areas is located in the vicinity of the wireless communication        device,    -   means for retrieving the position data of the reference area        located in the vicinity of said wireless communication device,    -   wherein for performing the positioning, the positioning system        comprises a selecting element for selecting said reference area        in the vicinity of the wireless communication device as the        default position of the wireless communication device.

According to a third aspect of the present invention there is providedan electronic device to be used in a positioning system, whichelectronic device comprises at least:

-   -   positioning means, and    -   mobile communication mean,    -   means for detecting which of the reference areas stored in the        data base of the positioning system is located in the vicinity        of the electronic device,    -   means for retrieving the position data of the reference area        located in the vicinity of the electronic device, and    -   means for selecting the reference area located in the vicinity        of said electronic device as the default position of the        electronic device in the positioning.

According to a fourth aspect of the present invention there is provideda wireless communication device to be used in a positioning system,which wireless communication device comprises at least:

-   -   positioning means, and    -   mobile communication means,    -   means for detecting which of the reference areas stored in the        data base of the positioning system is located in the vicinity        of the wireless communication device,    -   means for retrieving the position data of the reference area        located in the vicinity of the wireless communication device,        and    -   means for selecting the reference area located in the vicinity        of said wireless communication device as the default position of        the wireless communication device in the positioning.

According to a fifth aspect of the present invention there is provided acomputer program product for positioning of a wireless communicationdevice, the computer program product comprising machine executable stepsfor:

-   -   storing position data relating to one or a plurality of        reference areas to at least one data base,    -   examining which of said reference areas is located in the        vicinity of the wireless communication device, and    -   retrieving at least position data about said reference area        located in the vicinity of the wireless communication device,    -   wherein in order to perform the positioning, the computer        program product further comprises machine executable steps for        selecting said reference area located in the vicinity of the        wireless communication device as the default position of the        wireless communication device.

According to a sixth aspect of the present invention there is provided amethod for delivering assistance data for positioning of a wirelesscommunication device, the method comprising:

-   -   storing position data relating to one or a plurality of        reference areas to at least one data base,    -   examining which of said reference areas is located in the        vicinity of the wireless communication device, and    -   transmitting to the wireless communication device at least        position data about said reference area located in the vicinity        of the wireless communication device,    -   invoicing a user of the wireless communication device of the        transmitted assistance data.

According to a seventh aspect of the present invention there is provideda module to be used in an electronic device which module comprises atleast:

-   -   means for detecting which of the reference areas stored in the        data base of the positioning system is located in the vicinity        of the electronic device,    -   means for retrieving the position data of the reference area        located in the vicinity of the electronic device, and    -   means for selecting the reference area located in the vicinity        of said electronic device as the default position of the        electronic device for positioning of the electronic device.

Advantages can be achieved by the present invention when compared to thepositioning methods and receivers of prior art. Since the method of theinvention uses, as the default position of the electronic device, theposition of a reference point, for example a base station of a mobilecommunication network that is situated relatively close to theelectronic device, and auxiliary data is transmitted to the electronicdevice, the real position of the electronic device can be detectedrelatively fast. Additional advantages are provided in the method by thefact that the electronic device may store the auxiliary data andlocation data of the reference points it has received, wherein it is notalways necessary for the electronic device to detect this information byusing the mobile communication network, which reduces network traffic.In addition, this kind of retrieval of auxiliary data from a mobilecommunication network is usually subject to charge, wherein the costs ofthe positioning system paid by the user can be cut down by thearrangement of the invention. Yet another advantage to be mentioned isthat the decrease in network traffic can reduce also the powerconsumption of the electronic device, which is beneficial particularlyin portable electronic devices. The use of the method according to theinvention may allow in some situations positioning also indoors, whichis not necessarily possible with prior art solutions.

DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in more detailwith reference to the appended drawings, in which

FIG. 1 shows in a reduced manner a system in which the method accordingto a first embodiment of the invention can be applied,

FIG. 2 shows an electronic device according to a first embodiment of theinvention in a reduced block chart, and

FIG. 3 shows in a reduced manner a system in which the method accordingto a second embodiment of the invention can be applied,

FIGS. 4 a and 4 b depict examples of radiation patterns of anomnidirectional antenna and a directional antenna respectively

FIG. 5 a depicts a first example embodiment of the present invention asa simplified flow diagram,

FIG. 5 b depicts a second example embodiment of the present invention asa simplified flow diagram.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the operation of the method according to a firstexample embodiment of the invention will be described with reference tothe system shown in FIG. 1. An electronic device performing positioningis in FIG. 2 exemplified by a wireless communication device MScomprising, in addition to the mobile communication means MT, also apositioning receiver PR. Thus, the mobile communication means MT can beused for transmitting information between the wireless communicationdevice MS and the base stations BS, BS′, BS″ of the mobile communicationnetwork MN.

The base station BS, BS′, BS″ has an antenna 16 which can be anomnidirectional antenna or a directional antenna. When anomnidirectional antenna is used at the base station the base stationconstitutes one cell. Respectively, when a directional antenna is usedat the base station the base station constitutes more than one cell, onefor each sector of the directional antenna. The radiation pattern of theantenna 16 at least partly defines the coverage area of the cell. InFIGS. 4 a and 4 b examples of the radiation patterns of anomnidirectional antenna and a directional antenna are depicted,respectively. When the wireless communication device MS moves from onecell to another cell a handover is performed to change the serving cellfor the wireless communication device MS. Thus, it may happen that thebase station BS, BS′, BS″ remains the same although the serving cellchanges.

In a positioning receiver PR according to FIG. 2, a signal to bereceived via a first antenna 1 is converted for example to anintermediate frequency in the converter block 2. The signal converted tothe intermediate frequency comprises two components known as such: I andQ components, with a phase difference of approximately 90°there-between. These analog signal components converted to theintermediate frequency are digitized. During the digitizing of thesignal components, for example at least one sample is taken of eachchip, i.e. at least 1,023,000 samples per second are thus taken in theGPS system. Furthermore, the I and Q components of the digitized signalare multiplied by a signal formed by a first numerically controlledoscillator (NCO) 5. The purpose of the signal of this first numericallycontrolled oscillator 5 is to correct the frequency deviation caused bythe Doppler shift and a frequency error of the local oscillator (notshown) of the receiver. The signals formed in the converter block 2 arepreferably led to a digital signal processor 3. Reference codes ref(k)corresponding to the codes used in code modulation of the satellites tobe received at a time are generated in block 16. Using e.g. thisreference code ref(k), the positioning receiver PR attempts to find thecode phase and frequency deviation of the signal of the satellitereceived on each receiving channel, to be used in the operations afterthe synchronization.

A control block 7 is used for controlling inter alia a code phasedetector 9 which is used for adjusting the frequency of the numericallycontrolled oscillator 5, if necessary. The synchronization will not bedescribed in more detail in this specification, since it is prior artknown per se. If necessary, after the receiving channel has beensynchronized to the signal of a satellite SV1, SV2, SV3, SV4, thedemodulation and storage of the navigation information transmitted inthe signal can be initiated, if possible. The digital signal processor 3stores navigation information for example in a memory 4. In the methodaccording to the present invention, it is not necessary to modulate andstore this navigation information, but the positioning receiver PR hasto define the chip and epoch of the signals received from thesatellites.

The wireless communication device MS also comprises mobile communicationmeans MT for performing the functions of the wireless communicationdevice, such as a second antenna 10, a radio part 11, audio means, suchas a codec 14 a, a speaker 14 b and a microphone 14 c, a display 12, anda keypad 13. However, it is obvious that a part of the functional blocksof the wireless communication device MS can be common to both thepositioning receiver PR and the mobile communication means MT. Forexample the display 12 and the keypad 13 can be used in someapplications also in connection with the positioning receiver PR, forexample to show the result of the performed positioning. The controlblock 7 can also be common both for the control of the positioningreceiver PR and the mobile communication means MT, or one or a pluralityof individual control blocks can be arranged for both units.

In the mobile communication network MN every cell has an individualidentifier CGI (Cell Global Identity). For example in the GSM system thecell global identity CGI usually comprises the following four parts:

-   -   mobile country code MCC,    -   mobile network code MNC,    -   location area code LAC, and    -   cell identity CI.

When the base station BS, BS′, BS″ has an omnidirectional antenna thecoverage area of the base station constitutes one cell. However, basestations BS, BS′, BS″ in which directional antennas are used each sectorof the directional antenna can define one cell. Thus, the base stationBS, BS′, BS″ may in fact constitute more than one cell and each cell canbe identified by the individual identifier CGI of the cell.

Thus, every cell can be identified on the basis of the cell globalidentity CGI of this cell. The cell global identity CGI also identifiesthe base station BS, BS′, BS″. However, it may happen that the cellglobal identity CGI is not totally available or is partly unreadable forsome reasons. For example the cell identity CI is not available for thewireless communication device MS. In such a situation the wirelesscommunication device MS cannot identify the cell but it may use themobile country code MCC, the mobile network code MNC and/or the locationarea code LAC to get some estimate of the position of the wirelesscommunication device.

The serving cell, that is the cell of the base station BS, BS′, BS″,through which the wireless communication device MS communicates with themobile-communication network MN at a time, transmits to the mobilecommunication device the cell global identity CGI of the serving cell.The cell global identity can be transmitted, for example, via a controlchannel of the mobile communication network MN. Thus, inter alia inconnection with a cell handover the wireless communication device MN candetect the cell change on the basis of the change in the cell globalidentity CGI (block 500 in FIG. 5 a) if the cell identity CI isavailable. In the method according to the invention the location areacode LAC and also the mobile country code MCC and the mobile networkcode MNC of the cell global identity CGI are utilized in the followingmanner. In the wireless communication device MS the informationtransmitted by the base station BS, BS′, BS″ is received 501, from whichinformation inter alia on the cell global identity CGI or parts of it isfound out. According to this identity it is detected 502 whether anyinformation related to the position of this particular base station BS,BS′, BS″ is stored in the memory means 4, 8 of the wirelesscommunication device. If no positioning data in accordance with the cellglobal identity or the location area code LAC is found in the memorymeans 4, 8, the necessary positioning data is searched 504 from the database DB. In this embodiment the positioning data is stored in the mobilecommunication network MN, for example in each base station BS, BS′, BS″,in the mobile switching center MSC, or in the GPRS packet network. Thewireless communication device MS transmits 503 to the mobilecommunication network MN a request to transmit the positioning data ofthe base station in question to the wireless communication device MS. Itis not necessary to transmit the cell global identity of the basestation in the interrogation message because the mobile communicationnetwork knows through which base station the connection to the wirelesscommunication device is arranged at a time. As a response, the basestation transmits 505 the positioning data of the base station and, ifnecessary, other auxiliary data in accordance with the satellitepositioning system as well, such as the orbit parameters and the almanacdata of the satellites. The transmitted information is received in thewireless communication device MS, wherein at least the positioning dataof the base station is stored 506 in the memory means 4, 8. In addition,the received parts of the cell global identity CGI of the base stationare stored, which can then be used as an index to the positioning datastored into the memory means 4, 8. If the wireless communication deviceMS does not receive all the fields of the cell global identity CGI or ifthe base station BS does not for some reason send all of them, thewireless communication device MS checks which parts of the global cellidentity GCI the wireless communication device MS has received. If thereceived parts contain the location area code LAC, the mobile countrycode MCC and the mobile network code MNC, the wireless communicationdevice MS uses these data to determine the reference position to be usedin the positioning process.

The location area code LAC determines the area in which the cell and therespective base station BS is located. More than one cell and basestation BS can contain the same location area code LAC wherein theposition information, which the location area code LAC gives may not beso accurate than what is available if the cell identity CI were known,but the position information can still be accurate enough to help thepositioning receiver PR perform more accurate positioning. Even a coarsereference position can be helpful for starting signal acquisition in asatellite positioning receiver, if the receiver would not have otherwiseany information about the current position in the globe. Therefore, theposition information achievable by using the location area code LAC mayspeed up the operation of the positioning receiver PR in finding moreaccurate position information of the wireless communication device MS.

The position relating to the location area code LAC can be determined bya table, for example, which is defined by the operator of the mobilecommunication network. The same location area code may mean differentpositions in different mobile, communication networks. Therefore, themobile country code MCC and the mobile network code MNC are used to findout the correct interpretation of the location area code LAC. Theinterpretation table or other data for determining the position data onthe basis of the location area code LAC may be loadable via a basestation BS or it may have been stored into the wireless communicationdevice MS.

When the wireless communication device MS has determined the positiondata on the basis of the location area code LAC, the position of thereference point can be used by the positioning receiver PR to performmore accurate positioning 508.

An uncertainty measure can also be estimated, which relates to the sizeof location area. The location area includes all the cells (basestations) having the same location area code LAC. Because more than onecell can have the same location area code LAC, the uncertainty measurecan be greater when using only the location area code LAC compared tosituations in which also the cell identity CI is available.

The wireless communication device MS can have previously received andstored identity information of the same or another cell. The wirelesscommunication device MS can then use 507 the previously stored mobilecountry code MCC, the mobile network code MNC and the location area codeLAC if the cell global identity CGI is not available from the currentbase station. In many cases it can be assumed that the location of thewireless communication device has not changed too much since theprevious time when wireless communication device MS was able to receiveat least the mobile country code MCC, the mobile network code MNC andthe location area code LAC. Therefore, the previously received locationarea code LAC may give accurate enough estimation of the position forthe reference point to assist the positioning receiver PR perform thepositioning.

In some situations it will be sufficient that only the location areacode LAC is received from the serving cell. The reason for that is thatthe mobile country code MCC remains the same in the same country andalso the mobile network code MNC usually remains the same when thewireless communication device MS is operating inside the networkcoverage area. However, it may happen that if the wireless communicationdevice MS is not in its “home” country it may happen, that the servingcell varies between cells of different operators. This affects that themobile network code MNC also varies when the cell of another operatorbecomes the serving cell.

After the position of the serving cell is known in the wirelesscommunication device MS, it is possible to utilize this positioning dataof the respective base station in the positioning by setting it as thedefault position of the positioning receiver. According to thispositioning data the wireless communication device is informed of theapproximate position of the wireless communication device on the globe.On the basis of the time data transmitted by the base station it ispossible to estimate in the wireless communication device whichsatellites are above the horizon, that is, visible as seen from thewireless communication device. Next, the wireless communication devicecan attempt to search for the signals of these visible satellites.Positioning can thus be performed in a manner known as such by firstusing this default position and by precisioning the positioning on thebasis of the signals received from the satellites SV1 to SV4. Later inthis specification there will be described an example on how saidposition of a known reference point can be utilized in the positioning.

As a wireless communication device MS moves from the coverage area of acell to the coverage area of another cell (e.g. in FIG. 1 from thecoverage area of a first base station BS to the range of a second basestation BS′), the afore-mentioned detection of the cell data stored inthe storage means 4, 8 is performed in connection with the handover todetect whether any information on this second base station is stored inthe wireless communication device MS, or whether the information shouldbe retrieved from the data base DB. Next, preferably the position ofthis second base station BS′, if available, is used as the defaultposition of the wireless communication device MS in the positioning ofthe wireless communication device MS. If the cell identity CI of thesecond serving base station BS′ is not available then the location areacode LAC of the second serving base station BS′ is used to determine thedefault position of the wireless communication device MS. As it waspreviously mentioned, it may happen that the location area code LAC doesnot change although the change in serving base station changes.

On the other hand, if there is a change in the location area code LACbecause the wireless communication device MS moved from the coveragearea of one base station BS to the coverage area of a second basestation BS′, it is possible to use at this stage for example some otherpositioning data calculated on the basis of these two base stations, forexample the midpoint between centers of areas defined by these twolocation area codes, as the default position of the wirelesscommunication device MS. In this case, it is very probable that inconnection with a handover the wireless communication device MS ispositioned closer to this midpoint than to either of the base stationsBS, BS′. In this manner it is possible in some situations to fasterachieve the wished positioning precision in the positioning receiver MS.

In some mobile communication systems, such as systems based on the CDMA,the wireless communication device MS can simultaneously communicate withmore than one base station. Thus, as the default position of thewireless communication device MS can be used for example the positioningdata calculated according to the position of those base stations thatcommunicate simultaneously with the wireless communication device MS, ifavailable. For example, if three base stations are used in thecommunication, e.g. the geometric midpoint, which can be used as thedefault position, is calculated on the basis of the positioning data ofthese three base stations. It is obvious that the motion data of thewireless communication device MS can also be used in the definition ofthe default position, that is, in accordance with the previouslyperformed positionings the direction of movement of the wirelesscommunication device MS is estimated and, on the basis of this, attemptis made to select the base station positioned close to the direction ofmovement of the wireless communication device MS, e.g. the wirelesscommunication device is moving towards one of these base stations.

It is also possible to use other positioning data than the position ofthe base station as the default position of the wireless communicationdevice MS. For example, if the base station comprises more than onecell, a reference point (e.g. a center point) of the cell can beeevaluated for example on the basis of the positioning informationstored in the data base DB of the cell in question. It is also possiblethat the reference point is evaluated on the basis of the radiationpattern of the sector of the antenna which forms the cell in question.

In the above-described method according to a first example embodiment ofthe invention it was presumed that the data base used in the positioningdata of the base stations is located in the mobile communicationnetwork, wherein the positioning data can be retrieved from the mobilecommunication network. The positioning data can also be transmittedenciphered. In this case an enciphering code required in the decipheringis retrieved to the wireless communication device MS from the mobilecommunication network, for example as point-to-point messages. This kindof messaging is usually subject to a charge to the user of the wirelesscommunication device, wherein the user has to pay for the positioningdata of the location area codes LAC that he/she has retrieved. However,by using the method according to a first embodiment of the invention itis possible to decrease the need to retrieve auxiliary data, because theauxiliary data is stored in the memory means 4, 8 of the positioningreceiver at the stage when-new or changed data is received.

In the following, a method according to another example embodiment ofthe invention is described, in which auxiliary data is not retrievedfrom the mobile communication network, but from a data base DB providedelsewhere, e.g. in the Internet network 1. FIG. 3 illustrates, in areduced chart, a system in which this method according to a secondexample embodiment of the invention can be applied and FIG. 5 b depictsthe second example embodiment of the present invention as a simplifiedflow diagram. The data base DB is located in such an information networkor information system, which can communicate with a mobile communicationdevice. The data base DB is arranged for example in a data base server Sthat is connected to communicate with the Internet network I.Identification data and position information relating to location areacodes LAC are stored in the data base DB. Through the data base server Spossibly other auxiliary data of the satellite positioning system canalso be downloaded to the wireless communication device MS.

The communication connection set up from the wireless communicationdevice MS can be for example a connection according to a so-called WAPprotocol, by means of which the wireless communication device MS can beused for example for browsing information on the Internet network, interalia www pages of companies and other sites, where data is stored. Inthis case, from the memory means 4, 8 of the wireless communicationdevice MS the cell position data is retrieved 511, in accordance withwhich it is possible to communicate with said data base server S thatmaintains the data base DB for the positioning data of the cells. Inaddition to this position data the cell global identifier. CGI of thecell or part of it is detected, a message is formed 512, for example asa message or messages according to said WAP protocol, and transmitted513 to the mobile communication network, where the messages areconverted for example to messages according to the Internet Protocol andtransmitted further to the Internet network in a manner known as such.The identifier of the wireless communication device MS that hastransmitted the message is also added to the messages, wherein theresponse messages can be transmitted back to the communication devicethat has transmitted the interrogation message. Another example that canbe mentioned in this context is the use of short messages (SM) intransmission of positioning data and possible auxiliary data.

Setting up a communication connection with the data base server S can insome situations also be performed for example with a wireless local areanetwork WLAN. Thus, the wireless communication device MS creates acommunication connection with a wireless local area network, which, issituated in the vicinity of a wireless communication device MS andthrough which for example the Internet network I can be contacted.

In the Internet network the messages are transmitted to the targetaddress, in this case to the data base server S in which said data baseDB is located, by using the message transmission mechanisms of theInternet network, in a manner known as such. The data base serverinterprets the arrived message and detects 514, on the basis of the cellglobal identity CGI of the cell that has been transmitted in themessage, the information about this cell from the data base DB. Next,the data base server creates a response message comprising saidpositioning data, if positioning data related to said cell are stored inthe data base DB. Subsequently, the response message is transmitted 515from the data base server S to the Internet network 1, where the messageis routed to the mobile communication network MN. The mobilecommunication network transfers the response message to the base stationwhich is communicating with the wireless communication device at thetime. The base station sends the response message to the wirelesscommunication device MS. Next, in the wireless. communication device MSthe received positioning data is stored 516 into the memory means 4, 8,and the positioning is performed 517, if necessary.

In this method according to a second example embodiment of the inventionthe default position of the wireless communication device MS is alsodefined according to the positioning data of one or a plurality ofcells/base stations or location area codes LAC. When the wirelesscommunication device MS moves to the range of a cell, an interrogationmessage can be transmitted from the wireless communication devicerequesting the positioning data of said cell to be transmitted to thewireless communication device, in case the positioning data are not yetstored in the wireless communication device MS. This interrogationmessage is transferred to the data base server S, where it is detectedwhether the information related to said base station is found in thedata base DB. If the data are found in the data base DB, the data aretransmitted to the wireless communication device MS. The positioning canthereafter be performed in the positioning receiver PR by using thispositioning data of the cell as the default position or using theposition information relating to the location area code LAC if theposition of the cell is not available. In the same context, positioningdata of several cells and/or base stations BS, BS′, BS″ can betransmitted, and for example the data base server S finds out whichcells/base stations are positioned in the vicinity of said cell/basestation, e.g. the base station(s) of the adjacent cells. In this casethe data base server transmits to the wireless communication device MSalso positioning data of these cells/base stations positioned close tosaid cell/base station. However, if the cell identity CI is notavailable, the transmission of positioning data of these differentcells/base stations may be restricted to situations in which thelocation area codes of different base stations differ from each other.This arrangement provides the advantage that when the wirelesscommunication device MS is moving from the range of one cell/basestation to the range of a second cell/base station the wirelesscommunication device MS already has the positioning data of this secondcell/base station.

Even if an existing mobile communication network MN can also be utilizedin the transfer of the positioning data of the cells/base stations BS,BS′, BS″ in this embodiment, the positioning data are retrieved fromoutside the mobile communication network MN. The transfer service ofsuch positioning data of the cells/base stations BS, BS′, BS″ can bearranged to be independent of operators. Thus, service providers canthemselves price the service and, on the other hand, limit the use ofthe service if necessary. A service provider can be for example anInternet service provider, that gives preferably to registered users thepossibility to retrieve information from the data base DB.

In practice, the data base DB can be decentralized, wherein a pluralityof data base servers S of an embodiment of the invention can be locatedin different geographical locations. Thus, when a user arrives close tosuch a data base server S, a communication connection can be set upbetween the data base server S and the wireless communication device MS,for example by using a local communication method, such as a so-calledBluetooth or WLAN connection. Through this connection it: is possible totransfer for example the positioning data of one or a plurality ofreference points of the neighboring area to the wireless communicationdevice MS.

In addition to the positioning data of the cell/base station the defaultposition of the wireless communication device MS can also in someembodiments be the WLAN access point, the positioning data of which isknown and the signals transmitted by which have the necessaryinformation for the identification of the access point. The positioningdata of other short-range access points or the like, such as theBluetooth system, can be applied in connection with the method of theinvention if the, location of these access points is known and theaccess points can be identified in the wireless communication devices.

In some cases (for example Monaco) the country code expresses asufficiently small geographical area in view of the positioningaccording to the invention. The mobile network code MNC can also in somecases indicate the default position of the wireless communication deviceMS at a sufficient precision.

As was previously mentioned the directional pattern of the base stationantenna is not necessarily omnidirectional, but it can be directed tosome direction. Antenna structures are also known in which the directionof the directional pattern can be changed to a wished direction, forexample towards a wireless communication device in order to improve thesignal-to-noise ratio in this direction. The directional pattern canalso be composed of a plurality of segments directed to differentdirections. In these kind of situations the default position used is notnecessarily the position defined by the location area code LAC, but apoint within the location area determined according to the directionalpattern of the antenna of the base station, such as the center of thedirectional pattern. This can is some systems be calculated for examplein such a manner that the parameters of the directional pattern aretransmitted from the mobile communication network to the wirelesscommunication device, or the calculation is performed in the mobilecommunication network from which the location obtained as a result ofthe calculation is transmitted to the wireless communication device.

In the system according to a second example embodiment of the inventionthe information of the data base DB can be updated 509, 518 for exampleas follows. When a wireless communication device MS has successfullydetermined its position and is positioned inside the, location area of acell of a base station BS, or BS′, or BS″ (Note: MS is communicatingactively only with one BS, but it has knowledge about the neighbouringstations) and connected to this base station, the wireless communicationdevice transmits the information on its location, the location area codeLAC, the mobile country code MCC and the mobile network code MNC of thecell global identity CGI of the cell and advantageously also theinformation on timing advance TA, for example via the mobilecommunication network MN, to said data base server S in which the database DB is located. Thus, the data base server S updates information ofsaid cell in the data base DB according to the positioning datatransmitted from the wireless communication device MS. However, thisdata is not necessarily the precise position of the base station,because it is, nevertheless, not probable that the wirelesscommunication device MS would be positioned exactly at the base stationand because more than one base station may have the same location areacode LAC. However, these positioning data located in the coverage areaof the cell of the base station can be used as reference points, becausethese reference points are, nevertheless, relatively close to the basestation. In this case, a group of positioning data is stored into thedata base with the location area code LAC, the mobile country code MCCand the mobile network code MNC of the cell global identity CGI of saidcell, which data can be transmitted to the wireless communication deviceMS that has requested for the positioning data. When a plurality ofwireless communication devices having a positioning receiver performpositioning within the location area and transmit the information ontheir position to the data base server it is thus possible, on the basisof a set of data, to calculate e.g. a mean value, a geometric center orthe like, which is sent as the reference point to the wirelesscommunication device MS. In this case the position data of the BS's canalso be created by using the system. Moreover, this arrangement does notrequire that the operator of the mobile communication network would beinvolved in the system maintenance, that is, the system is operatorindependent.

Said advance timing data can be used in the data base server S in orderto estimate how close to said base station BS, BS′, BS″ the wirelesscommunication device MS is located. The smaller the advance timing thecloser to the base station the wireless communication device is normallylocated.

Wireless communication devices can transmit said positioning data andother information to the data base server S for example at regularintervals, or when a predetermined criterion is fulfilled, for examplewhen the location area code LAC is changed. Additionally, a local database containing information on the position of the data bases can becreated in the wireless communication device Mg. Thus, the wirelesscommunication device can transmit the positioning data of the basestations that it has stored to a second wireless communication deviceand/or to a data base server, for example as short messages, whereinthese data can be used also in the positioning functions of this second,wireless communication device and, on the other hand, the data base DBof the data base server is updated. The transmission of data to thesecond wireless communication device can be initiated e.g. by the userof the wireless communication device.

When describing above some embodiments of the invention it was notedthat the wireless communication device makes a request on thepositioning data of the cell while the wireless communication device islocated within the range of a certain cell. The invention can also beapplied in such a manner that the wireless communication device performsan information request for example when the positioning receiver PRand/or the mobile communication means MT are switched on. In this case,the information that relates for example to the position of cells/basestations BS, BS′, BS″ in a certain geographical area can be transmittedto the wireless communication device MS, and the information can be usedwithout a delay at the stage when the wireless communication device MSis moving within the range of the mobile communication network. Thus, itis not necessary to waste time for the transfer of base station data,but the information already exists stored in the memory means 8 of thewireless communication device. This, in its part, cuts down the powerconsumption of the wireless communication device MS and also decreasesthe load to the mobile communication network MN, because the need fordata transfer is diminished. It is obvious that this alternative alsoallows to detect which base station data is already stored in thewireless communication device MS, whereby it is not necessary totransfer these data again, unless there has been changes in the data.

By using the above-described method, the positioning can be performedalso in poor signaling conditions. Also, no precise time data isrequired if the position of the reference point is known. Moreover, thetransmission of auxiliary data is not dependent on the positioningservices provided by the operator.

In the following, an example is given on how said positioning datadefined on the basis of the location area code LAC can be used in thepositioning of a wireless communication device. In the definition oftime of transmission ToT according to the formula (1), only the numberand code phase T_(chip) ^(j)(k) of the chips received after the epochchange can be defined in a situation in which the strength of the signalto be received is weak. By means of this parameter it is possible tomeasure only the differences on the chip level (<1 ms) in the signals ofdifferent satellites SV1, SV2, SV3, SV4, because the same code isrepeated at intervals of one epoch (=1 ms). Because the distance betweeneach satellite and receiver can differ significantly, there may be largedifferences, even differences over 10 ms, in the times of flight ofsignals received from different satellites. Thus, the definition of thedifferences on the chip level is not sufficient. One millisecond in timerepresents a distance of approximately 300 km when the signal propagatessubstantially at the speed of light. Correspondingly, one chip(approximately 1 μs=1 ms/1023) equals approximately 300 meters.

In such a situation the differences of milliseconds have to be definedin different receiving channels on the basis of the distances betweenthe satellites SV1, SV2, SV3, SV4 and the wireless communication deviceMS. However, generally the estimated location of the wirelesscommunication device MS is not necessarily known. Instead, in thesystems according to FIGS. 1 and 3 it is possible to estimate thelocation of the wireless communication device MS by using a selectedreference point, such as the location of the base station BS. Thus, the,positioning data of the base station BS, BS′, BS″,the orbit parametersof the satellites SV1, SV2, SV3, SV4, and the time data stored into thememory means 4, 8 can be used in the wireless communication device MS.In the GSM mobile communication system the distance between the wirelesscommunication device and the base station with which the wirelesscommunication device is communicating at the time is generally about 30kilometers at the most. In this case it can be assumed that the wirelesscommunication device MS is located within a radius of 30 kilometers fromthe location of the base station BS. Thus, the time of flight of thesignal transmitted by the satellite from the satellite to the basestation and the time of flight from the satellite to the wirelesscommunication device differ approximately 100 its at the most. Thedistance between the wireless communication device MS and the basestation BS in view of the times of flight does not change to asignificant degree either within the base station BS range, wherein itcan be assumed that there is a difference of less than one millisecondin the reception times of the same signal in the wireless communicationdevice MS and in the base station BS. Thus, the distance can becalculated at an accuracy of one millisecond as follows: $\begin{matrix}{{{\hat{N}}_{ms}^{j}(k)} = \left\lceil \frac{{{{\overset{\_}{x}}_{SV}^{j}(k)} - {\overset{\overset{\_}{\hat{}}}{x}}_{u}}}{c} \right\rceil} & (2)\end{matrix}$in which ┌.┐ indicates rounding up to the nearest integer, and the lineabove the variable indicates that it is a vector. In this case, the sameresult is obtained both in view of the base station BS and in view ofthe wireless communication device MS. It has been possible to transmitfrom the base station BS a sort of estimate of the GPS time {circumflexover (T)}_(GPS) to the wireless communication device MS. If this GPStime data is very precise, it is also possible to calculate the positionof the satellites very accurately, wherein errors in positioning canmainly be caused by the distance between the wireless communicationdevice MS and the base station BS, which is not necessarily known. Evenif no time data were transmitted from the base station to the wirelesscommunication device, the wireless communication device contains somekind of arm estimation of the GPS time {circumflex over (T)}_(GPS), e.g.the time of the reference clock 15, which, at this stage, can be severalseconds, even minutes fast or slow.

After the distance {circumflex over (N)}_(ms) ^(j)(k) in time has beencalculated in milliseconds for all receiving channels according toformula 2, it is possible to estimate the times of transmission of thesignals according to the following formula.{circumflex over (T)} _(ToT) ^(j)(k)=T _(GPS) ^(j)(k)−{circumflex over(N)} _(ms) ^(j)(k)+T _(chip) ^(j)(k)   (3)

Any measured value of the time of transmission of the satellite signalcan be selected as the reference time. The time of the satellite at thetime of reception, i.e. the GPS time, {circumflex over (T)}_(GPS)(k),can thereafter be estimated by supplementing the time of transmissionToT attained on the basis of the measurement selected as reference timewith the estimated transfer delay, i.e. the time of flight of the signalfrom the satellite to the receiver. The estimated transfer delay isusually 78 ms.{circumflex over (T)} _(GPS)(k)={circumflex over (T)} _(ToT)^(j)(k)+0.078   (4)

After the GPS time has been preliminarily defined, it is possible todefine the measured pseudoranges by subtracting the calculated times oftransmission of the signal from the estimated GPS time and multiplyingthe result with the speed of light in the following manner:ρ_(m) ^(k)=({circumflex over (T)} _(GPS) −T _(ToT) ^(j)(k))c   (5)in which c indicates the speed of light in a vacuum, the superscript kindicates from which satellite signal the measured value comes from(e.g. 1 to 4) and the subindex m indicates that the pseudorange is ameasured pseudorange, not an estimated one.

The estimated pseudoranges are calculated in relation to the location{circumflex over ({overscore (X)})}_(u) of the wireless communicationdevice MS and to the locations {overscore (x)}_(SV) ^(j)({circumflexover (T)}_(GPS)) of the satellites at an estimated time of transmissionToT. The selected default location of the wireless communication deviceis the location defined on the basis of the location area code LAC ofthe base station BS which is communicating with the wirelesscommunication device at the time. The locations of the satellites arecalculated as a function of time by means of equations known as such.Here, for the sake of simplicity, the estimated pseudoranges areexpressed by means of the following formula:ρ_(ρ) ^(k) f({circumflex over (T)} _(GPS), {circumflex over ({overscore(x)})}_(u))   (6)to indicate that the estimated pseudoranges are based solely on theestimated GPS time and to the estimated location of the wirelesscommunication device. In formula (6), the term f represents a (strongly)non-linear function, the subindex p indicates that this is estimation,and {circumflex over ({overscore (x)})}_(u) is the estimated location ofthe wireless communication device, in which the line above the variableindicates that it is a vector.

The location {circumflex over ({overscore (x)})}_(u) of the wirelesscommunication device and the difference between the estimated GPS timeand the real GPS time can be calculated iteratively for example by theleast mean squares method. This method is known as such. In the leastmean squares method the following set of equations is solved:ρ_(m) ^(k) =∥{overscore (x)} _(SV) ^(j)(k)−{circumflex over ({overscore(x)})} _(u) , j=1 . . . M   (7)

The aim is to find such location data {circumflex over ({overscore(x)})}_(u) and time error Δt_(u), which best suit to a number M ofmeasurements. The solution of this set of equations is straightforwardas such: $\begin{matrix}{\begin{bmatrix}{{\Delta{\overset{\overset{\_}{\hat{}}}{x}}_{u}}\quad} \\{\Delta\quad t_{u}}\end{bmatrix} = {\left( {H^{T}H} \right)^{- 1}H^{T}\Delta\overset{\_}{\rho}}} & (8)\end{matrix}$in whichΔ{overscore (ρ)}={overscore (ρ)}_(m) ^(j)−{overscore (ρ)}_(ρ) ^(j) , j=1. . . M   (9)

-   -   Δ{circumflex over ({overscore (x)})}_(u) is the correction        vector of the location,    -   Δt_(u) is the correction of the time error,    -   and    -   H=the linearized Jacob's matrix of the pseudoranges estimated in        point {circumflex over ({overscore (x)})}_(u).

The solution given by the least mean squares method is optimal withrespect to the, sum of squared errors (SSE). This sum of squared errorscan be estimated by means of a formula: $\begin{matrix}{{SSE} \cong {\left( {{\Delta\overset{\_}{\rho}} - {H\begin{bmatrix}{{\Delta{\overset{\overset{\_}{\hat{}}}{x}}_{u}}\quad} \\{\Delta\quad t_{u}}\end{bmatrix}}} \right)^{T}\left( {{\Delta\quad\overset{\_}{\rho}} - {H\begin{bmatrix}{{\Delta{\overset{\overset{\_}{\hat{}}}{x}}_{u}}\quad} \\{\Delta\quad t_{u}}\end{bmatrix}}} \right)}} & (10)\end{matrix}$

By rearranging the terms and using slightly different expressions-forthe terms, it is possible to write the formula (7) in the followingmanner:ρ_(m) ^(j)(T _(GPS))=∥{overscore (x)} _(SV) ^(j)({circumflex over (T)}_(GPS))−{circumflex over ({overscore (x)})}_(u) ∥+ct _(u) , j=1 . . . M  (11)

The parentheses indicate that the term in question is based on theparameter presented in the parentheses. When such a presentation mode isused, it can clearly be seen that the measured pseudoranges arefunctions of the real GPS time and the rest of them are functions of theestimated GPS time. Thus, the time difference between the estimated GPStime and the actual GPS time can be calculated according to themeasurements, and in this case it is also possible to synchronize thereceiver to the actual GPS time. The time error of the receiver can herebe expressed as the time difference according to the following formula:Δt _(u) ≅ΔT=T _(GPS) −{circumflex over (T)} _(GPS)   (12)in which Δt_(u) represents the estimated time (or calculated) clockerror, and ΔT is the actual clock error between the estimated time,{circumflex over (T)}_(GPS), and the real GPS time.

It is now possible to use this time difference in a wirelesscommunication device MS to correct the estimated GPS time, whereafter itis possible to better calculate the satellite locations in order toperform positioning particularly in a situation where the calculatedtime difference is significant.

The calculation of distance as described above in formula 2 can in somesituations cause rounding errors. For example, if the distance inmilliseconds prior to rounding down is close to the next integer and thewireless communication device MS is close to a base station BS, an errorclosing to one millisecond can occur. This can mean an error of up to300 km when calculating the distance between the wireless communicationdevice and the satellite, which distorts the positioning to asignificant degree. In some cases, this error can be detected from theheight data calculated for the position of the wireless communicationdevice, which height data indicates that the wireless communicationdevice is located at an altitude of tens of kilometers or deep below theground. In this case, the error is easy to verify. However, this is notalways the case. The method according to an example embodiment of theinvention utilizes the information that the wireless communicationdevice MS is close to the base station BS, the position of which isknown at a sufficient precision. In this manner, it is possible to setthe limits within which the positioning data calculated for the wirelesscommunication device MS should be. This limit is in the direction of theearth's surface e.g. a base-station-centered circle having a radius ofapproximately 30-50 km. Correspondingly, appropriate limit values can bedefined in the elevation. If the calculation gives to the wirelesscommunication device MS a positioning data that is outside said limit,it can be assumed-that the rounding has caused an error. Subsequently,it is determined at which satellite/satellites the error has occurred.This can be performed by examining the remainders of the valuescalculated with the formula 2.

By using this method it is possible to fast detect the possible errorscaused by rounding and to perform the necessary corrective actions.Another method for detection of rounding errors is to examine the errorvalues calculated with formula 9 and if a value differs clearly from theother values (is significantly larger), the rounding has probably causedthe error in the calculation of the distance of the satellitecorresponding to said value.

The invention can be implemented at least partly as a software, forexample as machine executable steps in a program code of the controlblock 7 and/or the digital signal processor 3. Some parts of thesoftware can also be implemented in the mobile communication network MNand/or the server S.

The user of the wireless communication device may be invoiced of theassistance data (e.g. the location area code LAC) transmitted to thewireless communication device for the positioning.

It is obvious that the present invention is not limited solely to theabove- presented embodiments, but it can be modified within the scope ofthe appended claims.

1. A method for positioning of a wireless communication device, themethod comprising: storing position data relating to one or a pluralityof reference areas to at least one data base, examining which of saidreference areas is located in the vicinity of the wireless communicationdevice, and retrieving at least position data about said reference arealocated in the vicinity of the wireless communication device, wherein inorder to perform the positioning, the method further comprises selectingsaid reference area located in the vicinity of the wirelesscommunication device as the default position of the wirelesscommunication device.
 2. The method according to claim 1, saidretrieving comprising transmitting said position data to the wirelesscommunication device.
 3. The -method according to claim 1, comprisingusing one of the following as the reference area: a location area codeof a cell of a mobile communication network; a mobile country code; amobile network code; and when storing the position data of the referenceareas different reference areas are separated-in accordance with saidreference area.
 4. The method according to claim 3, comprisingestablishing a data base in the mobile communication network.
 5. Themethod according to claim 3, comprising setting up a communicationconnection between the wireless communication device and the basestation of the mobile communication network, and using the location areacode of a cell of the base station that communicates with the wirelesscommunication device at the time as the default position.
 6. The methodaccording to claim 3, comprising transmitting the position data of thecell of the base station from the base station to the wirelesscommunication device.
 7. The method according to claim 3, comprisingsetting up the data base in the data base server and establishing acommunication connection from the data base to the wirelesscommunication device to transfer position data between the wirelesscommunication device and the data base.
 8. The method according to claim7, comprising using a connection according to the WAP protocol as saidcommunication connection.
 9. The method according to claim 1, comprisingstoring information on the position of the reference areas also in thewireless communication device.
 10. The method according, to claim 9,comprising transmitting the cell global identity of the cellcommunicating with the wireless communication device to the wirelesscommunication device, wherein when the identity of the cell changes, anexamination is performed in the wireless communication device todetermine whether any position data based on the identity of the newcell are stored in the wireless communication device, wherein in case noposition data based on the identity of the new cell is stored in thewireless communication device, the method comprises sending a requestfrom the wireless communication device for transmission of positioningdata to the wireless communication device.
 11. The method according toclaim 1, comprising performing positioning for determining the positiondata of the reference areas position at least in one wirelesscommunication device, and transmitting the determined position data andthe identity of the base station to be stored into the data base.
 12. Apositioning system to be used in the positioning of a wirelesscommunication device, the positioning system comprising: at least onedata base for storing one or a plurality of reference areas, means fordetecting which of said reference areas is located in the vicinity ofthe wireless communication device, means for retrieving the positiondata of the reference area located in the vicinity of said wirelesscommunication device to the wireless communication device, wherein forperforming the positioning, the positioning system comprises a selectingelement for selecting said reference area in the vicinity of thewireless communication device as the default position of the wirelesscommunication device.
 13. The positioning system according to claim 12,wherein said means for retrieving the position data of the referencearea comprise means for transmitting the position data to the wirelesscommunication device,
 14. The positioning system according to claim 12,wherein the base stations of the mobile communication network arearranged to be used as the reference areas, for which a cell globalidentity is defined, and when storing the position data of the referenceareas different reference areas are separated from each other accordingto said identity.
 15. The positioning system according to claim 12,wherein the data base is established in the mobile communicationnetwork.
 16. The positioning system according to claim 14, comprisingmeans for establishing a communication connection between the wirelesscommunication device and the base station of the mobile communicationnetwork, wherein the selected default position is the position of thatbase station that communicates with the wireless communication device atthe time.
 17. The positioning system according to claim 14, wherein itcomprises means for transmitting position data of the base stations ofthe mobile communication network from the base station to the wirelesscommunication device.
 18. The positioning system according to claim 14,wherein the data base is set up in the data base server, and thepositioning system comprises means for setting up a communicationconnection from the data base to the wireless communication device totransfer position data between the wireless communication device and thedata base.
 19. The positioning system according to claim 18, whereinsaid communication connection is a connection according to the WAP,protocol.
 20. The positioning system according to claim 19, wherein thewireless communication device comprises memory for storing informationon the position of the reference areas.
 21. The positioning systemaccording to claim 20, comprising means for transmitting to the wirelesscommunication device the cell global identity of the cell with which thewireless communication device is communicating, wherein the wirelesscommunication device comprises means to examine when the location areacode changes whether the position data based on the new location areacode is stored in the wireless communication device, wherein in case nodata is stored in the wireless communication device, the wirelesscommunication device is adapted to transmit a request for transmittingposition data to the wireless communication device.
 22. The positioningsystem according to claim 12, wherein the wireless communication devicecomprises means for performing positioning, and means for transmittingthe defined position data and the location area code of the basestation, and that the positioning system comprises means for receivingsaid positioning data and location area code transmitted from thewireless communication device and for storing them into the data base.23. An electronic device to be used in a positioning system, whichelectronic device comprises at least: positioning means, and mobilecommunication means, means for detecting which of the reference areasstored in the data base of the positioning system is located in thevicinity of the electronic device, means for retrieving the positiondata of the reference area located in the vicinity of the electronicdevice, and means for selecting the reference area located in thevicinity of said electronic device as the default position of theelectronic device in the positioning.
 24. A computer program product forpositioning of a wireless communication device, the computer programproduct comprising machine executable steps for: storing position datarelating to one or a plurality of reference areas to at least one database, examining which of said reference areas is located in the vicinityof the wireless communication device, and retrieving at least positiondata about said reference area located in the vicinity of the wirelesscommunication device, wherein in order to perform the positioning, thecomputer program product further comprises machine executable steps forselecting said reference area located in the vicinity of the wirelesscommunication device as the default position of the wirelesscommunication device.
 25. A wireless communication device to be used ina positioning system, which wireless communication device comprises atleast: positioning means, and mobile communication means, means fordetecting which of the reference areas stored in the data base of thepositioning system is located in the vicinity of the wirelesscommunication device, means for retrieving the position data of thereference area located in the vicinity of the wireless communicationdevice, and means for selecting the reference area located in thevicinity of said wireless communication device as the default positionof the wireless communication device in the positioning.
 26. A methodfor delivering assistance data for positioning of a wirelesscommunication device, the method comprising: storing position datarelating to one or a plurality of reference areas to at least one database, examining which of said reference areas is located in the vicinityof the wireless communication device, and transmitting to the wirelesscommunication device at least position data about said reference arealocated in the vicinity of the wireless communication device, invoicinga user of the wireless communication device of the transmittedassistance data.
 27. A module to be used in an electronic device whichmodule comprises at least: means for detecting which of the referenceareas stored in the data base of the positioning system is located inthe vicinity of the electronic device, means for retrieving the positiondata of the reference area located in the vicinity of the electronicdevice, and means for selecting the reference area located in thevicinity of said electronic device as the default position of theelectronic device for positioning of the electronic device.